Islamic State terrorists singled out American journalist James Foley for brutal beatings and mock executions — including a posed crucifixion — when they learned his brother served in the US Air Force, according to fellow reporters held hostage with Foley before his grisly beheading.

“Because of that and as he was American he got extra bad treatment,” French journalist Nicolas Henin, who was imprisoned with Foley and later released, told France’s Express magazine.

“He became the whipping boy of the jailers, but he remained implacable.”

Another French journalist, Didier Francois, told the French i-Tele TV network that during one especially horrific incident, Foley was “made to pose as if he was being crucified against a wall,” The Telegraph reported.

Francois said the terrorists learned about Foley’s family ties to the US military through photos found on his computer of his younger brother John, 35.

Foley, 40, was kidnapped in November 2012 while leaving an Internet cafe in the Syrian city of Idlib, Francois said.

Didier FrancoisAFP/Getty Images

Francois was held hostage with Foley from last August until April, when he was released with three other French captives. He was also imprisoned for nine months with American journalist Steven Sotloff, who is still being held and was dragged before the camera and threatened with death in the same video that showed Foley’s brutal murder.

“[Foley] was an extraordinary person with a strong character. He was a pleasant companion in detention because he was solid and collective. He never gave in to the pressure and violence of the kidnappers,” Francois told Reuters.

The veteran journalist said he shared a cell with Foley starting in October and might be able to identify the jihadist in the gruesome video of Foley’s death.

When asked by radio station Europe 1 if he could recognize the masked Islamic State man, he said: “Recognized is a very big word. I see roughly who it is.”

This is the first time Francois has spoken out about his time as a hostage. He feared that guards would punish the prisoners left behind if he shared his story.

“Their exact words were: ‘They’ll be punished,’” he said.

Henin, who spent seven months in captivity with Foley, portrayed the dedicated journalist as a generous fellow prisoner who wouldn’t hesitate to share his blankets and food with others.

“You develop some kind of survival instinct (as a kidnap victim), meaning that for instance you try to grab everything you can find and James was the total opposite,” Henin told the BBC. “Basically, everything he could share he would share.”

On Thursday, U.S. Attorney General Eric Holder announced that the Justice Department is opening a criminal investigation into Foley’s gruesome murder.

“We will not forget what happened, and people will be held accountable, one way or another,” he said.